Separation patterns between Brazilian nut and reversed Brazilian nut of a binary granular system

Motion behaviour of ellipsoidal granular system under vertical vibration and airflow

We studied the motion behaviour of ellipsoid particles under vertical vibration and airflow. Three typical convection patterns were observed when submitted to vertical vibration with frequency (f) from 20 Hz to 80 Hz and dimensionless vibration acceleration (Γ) from one to six. We studied the effects of f and Γ on the change of convection patterns. We quantitatively studied the effects of f, Γ, airflow direction, airflow velocity, and particle shape on the convection area and intensity using the area fraction λ and average velocity vz characterizing the convection area and intensity, respectively. Results showed that the convection first occured occurred in the upper part of the granular system. Increasing f and A can both increase the convection area and strengthen the convection intensity. A had a greater influence than f at the same Γ. The wheat particles were more likely to enter the global convection state under the action of the airflow in the opposite direction of gravity. The maximum convection intensity of wheat particles under the airflow in the opposite direction of gravity was approximately 30-35% of the value measured under the airflow along the direction of gravity. The convection area and maximum convection intensity of the spherical particles were approximately 85% and 93% of the measured values for the ellipsoidal particles, respectively. We also analysed the effects of f, Γ, airflow direction, airflow velocity, and particle shape on the convection area on the basis of energy dissipation.

Diversity and controllability of particle distribution under coupling vibration and airflow

The vertical, horizontal, and three-dimensional (3D) distribution of binary particles with different diameters are investigated simultaneously in a cylindrical container under coupling vibration and airflow. Airflow is blown into the vertically vibrating granular bed from its bottom with vibration frequency of f = 15, 30, and 45 Hz; vibration acceleration Γ = 2-7; and air velocity u = 0-1.82 m s^-1 (fluidization number u/u_mf = 0-1.49). In our experiments, several distribution states have been observed, such as the mixing state, where particles are uniformly mixed; Brazil nut separation (BN), where large particles rise to the top; reverse Brazil nut separation (RBN), where large particles sink to the bottom; horizontal separation (HS), where binary particles separate horizontally; and combined distribution of BN/RBN and HS, in which one type of particles is above the other and close to one side of the container wall. Briefly, the vertical distribution forms five pattern types, and the horizontal distribution has four pattern types. The resultant pattern of 3D distribution exhibits 15 pattern types. These patterns can be always obtained under the conditions of certain control parameters, but the condition differs with the diameter ratio of binary particles. Phase diagrams of vertical, horizontal, and 3D distributions are drawn to provide the excitation condition of various patterns. These experimental results contribute to the further understanding of the entire distribution of particles and the control of particle distribution for different industry requirements.

Granular core phenomenon induced by convection in a vertically vibrated cylindrical container

A mixture of 13X molecular sieve (13XMS) particles and glass particles with identical diameters is placed in a cylindrical container. Under vertical vibration, heavier glass particles tend to cluster and are wrapped inside the convection of 13XMS particles, resulting in the granular core phenomenon. The vibration frequency f strongly influences particle convection and particle cluster modes. By contrast, the effect of the dimensionless acceleration amplitude Γ can be neglected. For different f ranges, the granular core is classified as center-type and ring-type cores. For the center-type core, heavy particles are distributed as an approximate zeroth-order Bessel function of the first kind in the radial direction and an exponential function in the height direction. For the ring-type core, the concentration of heavy particles follows the power-series function in the radial direction. A granular transport model is then established based on heavy-particle movements under steady state to analyze the effect of vibration parameters and granular convection on density segregation.

Convecting particle diffusion in a binary particle system under vertical vibration

We studied the separation behaviour of binary granular particles in a vertically vibrated container. The final separation of the binary particle system exhibited the Brazil-Nut (BN) effect, though it was not complete. Particle convection occurred, and four different typical convection modes were observed when the frequency f changed from 20 Hz to 80 Hz at constant dimensionless acceleration Γ = 4πAf(2)/g. However, when Γ changed from 2 to 4 at constant f, the system's convection mode stayed almost the same. In our experiments, one type of particle generally moved much faster than the other, so the former was termed the 'convecting' particle, and the latter was termed the 'non-convecting' particle. To study the separation results qualitatively, we divided the system into vertical layers and calculated the mass distribution of the binary particles along the z axis. The results showed that when f increased at constant Γ or Γ decreased at constant f, the convecting particles, usually the smaller and lighter ones, distributed less to the top side and more to the bottom side of the container. Finally, to explain the experimental results, we derived a mass conservation equation for the convecting particles considering simultaneous convection and diffusion. The equation described the experimental results well. We also analysed the effects of f, Γ, diameter ratio, density ratio, etc., on the final separation results.